Optical digital‐to‐analogue conversion for 2‐bit BPSK‐modulated signal based on delay line interferometer with balanced photodetector

Abstract

Optical digital-to-analogue (DA) conversion has the potential to realise fully-transparent optical communication systems, as it is considered to be fundamental in the most of operations, including packet switching and label processor. However, most DA converters have been confined to on–off keying modulation as opposed to phase-shift keying (PSK) modulation. In this Letter, the author provides an optical DA converter for binary PSK (BPSK) signal. The proposed scheme converts a digitised information into an optical intensity by using delay line interferometer and balanced photodetector. The scheme generates a quadrature PSK (QPSK) signal from two BPSK signals, then, the generated QPSK signal is coupled with a -shifted signal. The four constellations of the QPSK signal are converted into four levels at equal intervals when the angle is set at and . It is concluded that the optical 2-bit DA conversion is experimentally demonstrated for BPSK signal at 10 Gbps.